Image coding apparatus, image coding method, image decoding apparatus, image decoding method, and program

Abstract

An image coding apparatus configured to divide an image into one or more slices each including a plurality of blocks and to code each slice on a block-by-block basis includes a first coding unit configured to code blocks included in a first portion of the slice, and a second coding unit configured to code blocks included in a second portion of the slice, wherein, when the second coding unit codes an initial block in the second portion, the second coding unit codes the initial included in the second portion by referring to a first quantization parameter provided to the slice as an initial value and referred to by the first coding unit when the first coding units codes the initial block in the first portion.

The invention claimed is: 
     
       1. An image coding apparatus which generates a bitstream which is to be decoded by an image decoding apparatus, the image coding apparatus comprising:
 an acquisition unit configured to acquire image data; and 
 a coding unit configured to code the image data into the bitstream using quantization parameters, wherein, the coding unit is configured:
 to code a difference value between a slice quantization parameter and a first quantization parameter of a first line in a slice, wherein the difference value is for the first quantization parameter of the first line, wherein the difference value is coded into the bitstream, and wherein the slice quantization parameter is provided to the slice; 
 to code a difference value between the first quantization parameter of the first line and a second quantization parameter of the first line, wherein the difference value is for the second quantization parameter of the first line, and wherein the difference value is coded into the bitstream; and 
 to code a difference value between the slice quantization parameter and a first quantization parameter of a second line in the slice, wherein the difference value is for the first quantization parameter of the second line, and wherein the difference value is coded into the bitstream. 
 
 
     
     
       2. The image coding apparatus according to  claim 1 ,
 wherein the coding unit codes a second quantization parameter of the second line using the first quantization parameter of the second line. 
 
     
     
       3. The image coding apparatus according to  claim 1 ,
 wherein the coding unit codes 
 a difference value between the first quantization parameter of the second line and a second quantization parameter of the second line, wherein the difference value is for the second quantization parameter of the second line, and wherein the difference value is coded into the bitstream. 
 
     
     
       4. The image coding apparatus according to  claim 1 ,
 wherein the coding unit codes a first block in the second line by referring to statistical information based on a result of entropy coding performed on a predetermined block in the first line in the slice. 
 
     
     
       5. The image coding apparatus according to  claim 1 ,
 wherein the coding unit comprises a first coding unit configured to code difference values of quantization parameters of the first line, and a second coding unit configured to code difference values of quantization parameters of the second line, and 
 wherein coding the difference values of quantization parameters of the first line, and coding the difference values of quantization parameters of the second line are performed in parallel. 
 
     
     
       6. The image coding apparatus according to  claim 5 ,
 wherein the first coding unit codes blocks in the first line using the quantization parameters of the first line, 
 the second coding unit codes blocks in the second line using the quantization parameters of the second line, and 
 wherein coding the blocks in the first line and coding the blocks in the second line are performed in parallel. 
 
     
     
       7. The image coding apparatus according to  claim 1 ,
 wherein, in a case where the coding unit performs a specific process on a block-line-by-block-line basis, the coding unit codes the first quantization parameter of the first line using the slice quantization parameter, and the first quantization parameter of the second line using the slice quantization parameter. 
 
     
     
       8. The image coding apparatus according to  claim 1 ,
 wherein the first quantization parameter of the first line is a quantization parameter which is first in a coding order of quantization parameters of the first line, 
 the second quantization parameter of the first line is a quantization parameter which is second in the coding order of the quantization parameters of the first line, 
 the first quantization parameter of the second line is a quantization parameter which is first in a coding order of quantization parameters of the second line, and 
 the second quantization parameter of the second line is a quantization parameter which is second in the coding order of the quantization parameters of the second line. 
 
     
     
       9. The image coding apparatus according to  claim 1 ,
 wherein the coding unit codes each of the quantization parameters in the first line other than the first quantization parameter in the first line, using a quantization parameter immediately before the each of quantization parameters in the first line. 
 
     
     
       10. An image decoding apparatus which decodes image data from a bitstream, the image decoding apparatus comprising:
 a derivation unit configured to derive quantization parameters based on difference values decoded from the bitstream; and 
 a decoding unit configured to decode the image data using the quantization parameters, wherein the derivation unit is configured:
 to derive a first quantization parameter of a first line in a slice by adding a difference value to a slice quantization parameter, wherein the difference value is a difference value between the slice quantization parameter and the first quantization parameter of the first line, and wherein the slice quantization parameter is provided to the slice; 
 to derive a second quantization parameter of the first line by adding a difference value to the first quantization parameter of the first line, wherein the difference value is a difference value between the first quantization parameter of the first line and the second quantization parameter of the first line; and 
 to derive a first quantization parameter of a second line in the slice by adding a difference value to the slice quantization parameter, wherein the difference value is a difference value between the slice quantization parameter and the first quantization parameter of the second line. 
 
 
     
     
       11. The image decoding apparatus according to  claim 10 ,
 wherein the derivation unit derives a second quantization parameter of the second line using the first quantization parameter of the second line. 
 
     
     
       12. The image decoding apparatus according to  claim 10 ,
 wherein 
 the derivation unit derives a second quantization parameter of the second line by adding a difference value to the first quantization parameter of the second line, wherein the difference value is a difference value between the first quantization parameter of the second line and the second quantization parameter of the second line. 
 
     
     
       13. The image decoding apparatus according to  claim 10 ,
 wherein the decoding unit decodes a first block in the second line by referring to statistical information based on a result of a process related to entropy coding performed on a predetermined block in the first line in the slice. 
 
     
     
       14. The image decoding apparatus according to  claim 10 ,
 wherein the derivation unit comprises a first derivation unit configured to derive quantization parameters of the first line, and a second derivation unit configured to derive quantization parameters of the second line, and 
 wherein derivation by the first derivation unit and derivation by the second derivation unit are performed in parallel. 
 
     
     
       15. The image decoding apparatus according to  claim 10 , further comprising:
 wherein the decoding unit comprises a first decoding unit configured to decode blocks in the first line using quantization parameters of the first line, and a second decoding unit configured to decode blocks in the second line using quantization parameters of the second line, and 
 wherein decoding the blocks in the first line and decoding the blocks in the second line are performed in parallel. 
 
     
     
       16. The image decoding apparatus according to  claim 10 ,
 wherein, in a case where the derivation unit performs a specific process on a block-line-by-block-line basis, the derivation unit derives the first quantization parameter of the first line using the slice quantization parameter, and the first quantization parameter of the second line using the slice quantization parameter. 
 
     
     
       17. The image decoding apparatus according to  claim 10 ,
 wherein the first quantization parameter of the first line is a quantization parameter which is first in a decoding order of quantization parameters of the first line, 
 the second quantization parameter of the first line is a quantization parameter which is second in the decoding order of the quantization parameters of the first line, 
 the first quantization parameter of the second line is a quantization parameter which is first in a decoding order of quantization parameters of the second line, and 
 the second quantization parameter of the second line is a quantization parameter which is second in the decoding order of the quantization parameters of the second line. 
 
     
     
       18. The image decoding apparatus according to  claim 10 ,
 wherein the deriving unit derives each of quantization parameters in the first line other than the first quantization parameter in the first line, using a quantization parameter immediately before the each of quantization parameters in the first line. 
 
     
     
       19. An image coding method which generates a bitstream which is to be decoded by an image decoding method, the image coding method comprising:
 acquiring image data; and 
 coding the image data into the bitstream using quantization parameters, wherein, the coding is configured:
 to code a difference value between a slice quantization parameter and a first quantization parameter of a first line in a slice, wherein the difference value is for the first quantization parameter of the first line, wherein the difference value is coded into the bitstream, and wherein the slice quantization parameter is provided to the slice; 
 to code a difference value between the first quantization parameter of the first line and a second quantization parameter of the first line, wherein the difference value is for the second quantization parameter of the first line, and wherein the difference value is coded into the bitstream; and 
 to code a difference value between the slice quantization parameter and a first quantization parameter of a second line in the slice, wherein the difference value is for the first quantization parameter of the second line, and wherein the difference value is coded into the bitstream. 
 
 
     
     
       20. An image decoding method which decodes image data from a bitstream, the image decoding method comprising:
 deriving quantization parameters based on difference values decoded from the bitstream; and 
 decoding the image data using the quantization parameters, wherein, the deriving is configured:
 to derive a first quantization parameter of a first line in a slice by adding a difference value to a slice quantization parameter, wherein the difference value is a difference value between the slice quantization parameter and the first quantization parameter of the first line, and wherein the slice quantization parameter is provided to the slice; 
 to derive a second quantization parameter of the first line by adding a difference value to the first quantization parameter of the first line, wherein the difference value is a difference value between the first quantization parameter of the first line and the second quantization parameter of the first line; and 
 to derive a first quantization parameter of a second line in the slice by adding a difference value to the slice quantization parameter, wherein the difference value is a difference value between the slice quantization parameter and the first quantization parameter of the second line. 
 
 
     
     
       21. A non-transitory computer-readable storage medium storing a program that causes a computer to execute an image coding method which generates a bitstream which is to be decoded by an image decoding method, the image coding method comprising:
 acquiring image data; and 
 coding the image data into the bitstream using quantization parameters, wherein, the coding is configured:
 to code a difference value between a slice quantization parameter and a first quantization parameter of a first line in a slice, wherein the difference value is for the first quantization parameter of the first line, wherein the difference value is coded into the bitstream, and wherein the slice quantization parameter is provided to the slice; 
 to code a difference value between the first quantization parameter of the first line and a second quantization parameter of the first line, wherein the difference value is for the second quantization parameter of the first line, and wherein the difference value is coded into the bitstream; and 
 
 to code a difference value between the slice quantization parameter and a first quantization parameter of a second line in the slice, wherein the difference value is for the first quantization parameter of the second line, and wherein the difference value is coded into the bitstream. 
 
     
     
       22. A non-transitory computer-readable storage medium storing a program that causes a computer to execute an image decoding method which decodes image data from a bitstream, the image decoding method comprising:
 deriving quantization parameters based on difference values decoded from the bitstream; and 
 decoding the image data using the quantization parameters, wherein, the deriving is configured:
 to derive a first quantization parameter of a first line in a slice by adding a difference value to a slice quantization parameter, wherein the difference value is a difference value between the slice quantization parameter and the first quantization parameter of the first line, and wherein the slice quantization parameter is provided to the slice; 
 to derive a second quantization parameter of the first line by adding a difference value to the first quantization parameter of the first line, wherein the difference value is a difference value between the first quantization parameter of the first line and the second quantization parameter of the first line; and 
 to derive a first quantization parameter of a second line in the slice by adding a difference value to the slice quantization parameter, wherein the difference value is a difference value between the slice quantization parameter and the first quantization parameter of the second line.